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Thread: Lead Substitue

  1. #1
    CB750 New Member Boston Fire Lt's Avatar
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    Lead Substitue

    A local guy who just went through my '71 CB750 (bought new) says no lead substitute is needed in these motors. Since leaded gas was eliminated in the mid 70s I have been using a substitute and StarTron stabilizer with 93 octane gas, usually Sunoco or Mobil. Any suggestions?

  2. #2
    CB750 Addict Dave's Avatar
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    Fuel "additives" are mostly scams, todays version of snake oil. Pump gas used to contain tetraethyl lead to help in the lubrication of the valve guides. Today we have better oil. You don't even need premium gas because the compression ratio is quite low on the old 750's but, I use it too because higher octane = more power and these old bikes don't have a lot HP compared to modern bikes.

    If you live in a small town with a local airport, you can go there with a gas can and purchase some avgas 100 (100 octane) or possibly find some avgas 100LL (leaded 100 octane). Be aware that it is illegal to use these fuels in ground vehicles and they will cause your engine to run at a much higher temperature.

    Note: The one fuel additive I personally know to work is Techron made by chevron. A bottle a month keeps the fuel injectors clean in modern engines.

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    Moderator dirtdigger's Avatar
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    Higher octane doesn't necessarily mean more power. If you can get by with 88 octane and have no ping, using a higher octane only costs you extra money in the cost of premium. That being said I only run 91 octane premium because the fuel itself is made from better stock than the lower grades and burns a little cleaner and is more consistent. If you do a fair amount of low speed and in town riding the premium will help with the ping tendency when the motor gets hotter then normal. The 750 on has about 9.2 : 1 compression depending on the year but they are all pretty close, the earlier the bike the more timing they had built into it also...71 is about the last of the "good" years. I have easily run 10.5 and little higher on compression and just run on premium 91 octane...no ping or knock. The 750 was made to run on unleaded fuel, they have harder exhaust seats and the valves are decent quality from the factory. Run premium and it you are afraid or think you may have gotten some bad gas add some octane boost but lead additive is not needed.

  4. #4
    CB750 Member Superseca92's Avatar
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    Quote Originally Posted by Dave View Post
    Fuel "additives" are mostly scams, todays version of snake oil. Pump gas used to contain tetraethyl lead to help in the lubrication of the valve guides. Today we have better oil. You don't even need premium gas because the compression ratio is quite low on the old 750's but, I use it too because higher octane = more power and these old bikes don't have a lot HP compared to modern bikes.

    If you live in a small town with a local airport, you can go there with a gas can and purchase some avgas 100 (100 octane) or possibly find some avgas 100LL (leaded 100 octane). Be aware that it is illegal to use these fuels in ground vehicles and they will cause your engine to run at a much higher temperature.

    Note: The one fuel additive I personally know to work is Techron made by chevron. A bottle a month keeps the fuel injectors clean in modern engines.
    Just to piggyback off of what dirt digger said; higher octane fuel doesn't increase horsepower at all. Higher octane gas may have a different quality than regular (maybe) but unless the service manual says otherwise, don't waste your money. I think the horsepower rumor came from people who NEED a higher octane to run normally. Higher compression engines require higher octane to prevent pre ignition along with a LOSS of horsepower, but unless you built up your engine to run a higher compression ratio, no need. That being said, there are tools you can use to check fuel quality if you really care that much about your baby. I run 87 with no additives in my 81 custom, but I do occasionally use seafoam once in a while and I plan on overhauling the engine in the next few years anyway lol. But seriously, save your money.

  5. #5
    CB750 New Member Boston Fire Lt's Avatar
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    I understand how premium will not increase power. In my 5 series BMW it does make a noticeable difference over the mid grade I usually use as the knock sensors allow advanced timing. In the bike I am using mid grade Mobil with some Startron added for the ethanol.

    The bike is running slightly rich, especially at idle. I'm waiting for the K&N air filter to come, the thinking being the additional air flow may negate the richness somewhat. Or should I turn the air screws out a bit (they are on the engine side of the carbs)?

  6. #6
    CB750 Member Superseca92's Avatar
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    I'd get the filters since it'd still be good idea for performance, but I wouldn't bank on it completely solving your issue, but it'll help. You'll still have to fine tune your settings as you may start to lean out a bit.

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    CB750 Addict Dave's Avatar
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    OK guys. I fill my tank with AV100 and my bike has a lot more power and runs hotter. If it's not the higher octane, then what is it?

    This also goes for brand name racing fuels.

    (PS not just this bike, any bike, and cars too. I used to run AV110 in my 70 Camaro and it reduced 1/4m ET's)

  8. #8
    CB750 Member Superseca92's Avatar
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    Quote Originally Posted by Dave View Post
    OK guys. I fill my tank with AV100 and my bike has a lot more power and runs hotter. If it's not the higher octane, then what is it?

    This also goes for brand name racing fuels.

    (PS not just this bike, any bike, and cars too. I used to run AV110 in my 70 Camaro and it reduced 1/4m ET's)
    All I can imagine is either they both were nodded for power therefore they benefit from high octane, or they were meant to run high octane from the beginning and switching made an increase.

  9. #9
    Moderator dirtdigger's Avatar
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    The reason it is hotter is it is probably running lean now with the av gas. Also California gas has more oxygen added then the rest of us and that causes other issues with power output etc. Same thing around here they add ethanol and I avoid that like the plague. AV gas has a lower density then crap street gas. AV gas is also made from a better stock as is with premium stated before. Better base stock will cause it to burn more efficient...more efficiency = more power...as well as causing it to run leaner if no other changes are made. Do some searching and you will find many engine builders dont recommend running straight AV gas as it causes issues with rings etc because it is "dry" compared to regular gas.
    Last edited by dirtdigger; 07-03-2015 at 04:18 PM.

  10. #10
    CB750 Addict Dave's Avatar
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    Thanks DD, your reply piqued my interest even more.

    I did find that running lower then recommended octane will reduce power but running higher won't increase it. As you said it's better gas that makes more power.

    I did already know av was "dry". I don't use it now but when I did I ran it about 80:1 with 2 stroke oil.

  11. #11
    CB750 Addict Dave's Avatar
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    Sorry for dbl post, some script is messing with my browser

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    CB750 New Member Riley14's Avatar
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    "The phase-down of lead in gasoline began in 1974 when, under the authority of the Clean Air Act Amendments of 1970, the U.S. Environmental Protection Agency (EPA) introduced rules requiring the use of unleaded gasoline in new cars equipped with catalytic converters."

    So I have a K1 (1971) and was made to run on gas with lead cause it was before the phase out so the unleaded fuel I use does not cushion the vales.

    All I want to know is a good Fuel Additive to put in my K1 that will help with this? I saw a suggestion about techron but is there any others worth my while?

    Thanks

  13. #13
    CB750 New Member Riley14's Avatar
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    "The phase-down of lead in gasoline began in 1974 when, under the authority of the Clean Air Act Amendments of 1970, the U.S. Environmental Protection Agency (EPA) introduced rules requiring the use of unleaded gasoline in new cars equipped with catalytic converters."

    So I have a K1 (1971) and was made to run on gas with lead cause it was before the phase out so the unleaded fuel I use does not cushion the vales.

    All I want to know is a good Fuel Additive to put in my K1 that will help with this? I saw a suggestion about techron but is there any others worth my while?

    Thanks

  14. #14
    CB750 Guru amc49's Avatar
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    There is absolutely NOTHING that can take the place of lead in older fuel, the stuff was a miracle chemical when they first began to add it to fuel. It does nothing for valve guides, rather it cushions the valve SEAT on exhaust to prevent seat recession. The hard coat on Honda valves prevents it up to a point but why you can't grind the valves, it removes that and the valves then die in only a few thousand miles, the seats will be utterly dead.

    I sold those additives for many years.....................anybody saying one replaces lead is incorrect, the maintenance chemical representatives actually encouraged rumors like that as it sold far more product. They when I pressed them would admit there was nothing in the products that helped with the valve problems at all and I asked a bunch of them back in the day. I was a bit of a sales rep gadfly.

    They've gotten around the issue since around '74 by extra hardening of valve seats and better steels used on the valves and even that can still be a bit short, I have valve recession issues on modern engines after '00, they just take like 75K miles to show instead of 10K. Take almost any higher mileage engine apart and you will find evidence of it. I grind the exhaust seats only to save money and it picks up an easy 10-15 hp. on the typical small fours many cars now use. The intakes will be OK and a light lap-in and they are ready to go.

  15. #15
    CB750 New Member Riley14's Avatar
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    Thank-you

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